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Influence of the bedrock on maar fragmentation processes

Rémy Jubertie 1, Lucia Gurioli1, Catherine Deniel1, Didier Miallier2, Simon Falvard1, Julien Bernard3,

  • Affiliations:  1 Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France 2 Université Clermont Auvergne, Laboratoire de Physique Corpusculaire, CNRS/IN2P3, Campus Universitaire des Cézeaux, TSA 60026, 63178 Aubière cedex, France 3 Bureau de Recherche Géologiques et Minières (BRGM), 3 Avenue Claude-Guillemin, BP 36009, 45060 Orléans CEDEX 2, France 

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 184

  • Programme No: 3.3.18

  • Theme 3 > Session 3

Abstract

Maars, that are the second most abundant terrestrial volcanic edifices, result from magma water interaction, also called MFCI (Molten Fuel-Coolant Interaction). As a result of this type of interaction, the intensity of the explosions is high despite the small volumes emitted. Furthermore, these explosions occurred in depth, excavating the substrate to form a diatreme. Consequently, the substrate is involved during the fragmentation process. In order to study the impact of the bedrock on maar fragmentation processes we focused on two maars whose emplaced into two distinct substrates. The first is the maar de Jaude (French Massif Central, France), located in soft sediments. The second, is the maar de Kawéni (Mayotte, France), situated in a hard volcanic bedrock. In addition, these two volcanic edifices are part of a quiescent volcanic province for the former and an active one for the latter. Field studies allowed us to reconstruct the eruptive scenario of each maar and identify interactions between the substrate and the magma. In the case of the edifice emplaced in a soft substrate, the interaction occurred between the magma and wet sediments. The explosivity in this type of mingling is damped compared to pure water-magma interaction. Besides, textural analyses of the vesicles and crystals permitted to characterize the pre-eruptive conditions of the magma. Indeed, the explosivity of phreatomagmatism is controlled by the water/magma mass or flux ratio. Thus, textural analyses bring constraints on the magma flux which should modulate the influence of the substrate on the fragmentation process.